Subsea equipment acoustic monitoring system

ABSTRACT

Systems and methods for monitoring subsea equipment are described herein. In one embodiment, such a system can include a plurality of acoustic sensor arrays that each include at least two acoustic sensors, wherein at least a first acoustic sensor array is mounted on an outer surface of subsea equipment being monitored and at least a second acoustic sensor array is positioned remote from the subsea equipment. The system can also include a digital data processor in communication with the plurality of acoustic sensor arrays, the digital data processor can be configured to process data from selected sensors of the plurality of acoustic sensor arrays to both selectively focus on a portion of the subsea equipment and to determine a point of origin of an acoustic signal. The system can be particularly useful in detecting leaks and other events in subsea drilling equipment.

PRIORITY

This U.S. Patent Application is a continuation of U.S. patentapplication Ser. No. 14/139,860, filed Dec. 23, 2013, entitled “SubseaEquipment Monitoring System,” which is hereby incorporated by referenceherein in its entirety.

FIELD

The present invention relates to subsea industrial activities and, inparticular, to systems and methods for monitoring subsea equipment, suchas oil and gas extraction equipment.

BACKGROUND

For many years, certain industrial activities, such as oil and gasextraction, have increasingly expanded to subsea locations, as thenumber of available land-based sites has declined. The seafloor,however, is a harsh and inaccessible environment, and many activities,e.g., drilling operations, involve considerable risk of environmentalcontamination. In some cases, an oil or gas well can be locatedthousands of feet below the surface of the water where no human can go.As a result, monitoring the safety and efficiency of drilling equipmentcan be difficult.

For example, in many cases the instruments used to monitor subseadrilling equipment (or other types of equipment) fail more often thanthe equipment itself. Failure of the monitoring instruments can createfalse positive warnings of drilling equipment failure, and cannecessitate excess maintenance procedures to fix the monitoring system.Furthermore, traditional monitoring instruments are often incorporatedinto the drilling equipment and, as a result, repairing the instrumentscan require a costly operation to bring the piece of equipment up fromthe seafloor. Moreover, even when monitoring instruments are operatingcorrectly, they provide little detail, e.g., allowing operators todetermine only whether a major event (e.g., a catastrophic componentfailure) has occurred.

Prior art systems have attempted to address the above issues, but withlittle success. For example, acoustic monitoring of subsea equipment hasbeen attempted using sensors mounted remotely from the subsea equipment,but these systems suffer from the same lack of detail discussed above.Accordingly, they provide little value to operators beyond reporting amajor event (e.g., a catastrophic component failure).

Given these shortcomings, monitoring instruments for subsea equipmentare often considered unreliable and not used. Without any ability tomonitor subsea equipment during operation, acceptable safety levels areachieved by building overly robust subsea equipment and implementingconservative maintenance schedules—both of which add considerable costto subsea operations.

Accordingly, there is a need in the art for improved subsea equipmentmonitoring systems that can provide more detailed monitoring ofequipment during operation. In addition, there is a need for suchsystems to have built-in redundancy and the ability to be servicedseparately from the subsea equipment to prevent unnecessary maintenancein the event of monitoring system failure.

SUMMARY

The present invention addresses these needs by providing systems andmethods for monitoring subsea equipment using a plurality of sensors anda digital data processor to analyze data collected by the sensors. Forexample, a system can include a plurality of acoustic sensors and thesignals detected by the sensors can be utilized to determine any of avariety of characteristics of the equipment (e.g., the rotation speed ofa drill, the presence of internal or external leaks, the presence ofworn seals or bearings, etc.). The systems described herein generallyinclude a plurality of acoustic sensor arrays both mounted on andpositioned remote from subsea equipment being monitored. The use ofmultiple arrays (each containing multiple acoustic sensors) positionedclose to, and remote from, equipment being monitored can allow thedigital data processor to isolate particular areas of the equipmentbeing monitored, or to locate an origin of a detected acoustic signal.Furthermore, the acoustic monitoring systems described herein canidentify particular acoustic signals associated with a physical event,e.g., the formation of a leak, etc., and track trends over time toidentify operational abnormalities. Finally, the increased amount ofacoustic data collected by the plurality of sensors provides a greateramount of detail than known monitoring instruments. This can allow, forexample, monitoring of individual seals, bearings, or other componentsto determine when replacement is necessary prior to catastrophiccomponent failure.

In one aspect, a system for monitoring subsea equipment includes aplurality of acoustic sensor arrays that each include at least twoacoustic sensors, wherein at least a first acoustic sensor array ismounted on an outer surface of subsea equipment being monitored and atleast a second acoustic sensor array is positioned remote from thesubsea equipment. The system also includes a digital data processor incommunication with the plurality of acoustic sensor arrays, and thedigital data processor can be configured to process data from selectedsensors of the plurality of acoustic sensor arrays to both selectivelyfocus on a portion of the subsea equipment and to determine a point oforigin of an acoustic signal. These abilities can allow a subseaequipment monitoring system to, for example, detect an irregular sound,locate the origin of the sound in or on the equipment being monitored,and selectively listen to that portion of the equipment. All of this ispossible even though the system might not include an acoustic sensor inthe immediate area of the portion being examined.

The enhanced monitoring capabilities of the systems described herein canbe combined with traditional equipment monitoring systems to confirmexpected operation of subsea equipment. For example, in one aspect, amethod for monitoring subsea drilling includes detecting acousticsignals generated by a drill using a plurality of acoustic sensor arraysthat each include at least two acoustic sensors, wherein at least afirst acoustic sensor array is mounted on an outer surface of a subseablowout preventer (BOP) surrounding the drill and at least a secondacoustic sensor array is positioned remote from the BOP. The method alsoincludes determining an operating characteristic of the drill within theBOP based on the detected acoustic signals using a digital dataprocessor that communicates with the plurality of acoustic sensorarrays. Further, the method includes detecting the operatingcharacteristic of the drill at a location above a surface of the sea, aswell as alerting a user via a user interface coupled to the digital dataprocessor if a difference between the characteristic value of the drillwithin the BOP and the characteristic value of the drill above thesurface of the sea is greater than a predetermined amount. For example,if the operating characteristic being measured is the rotation speed ofa drill, a difference between speeds measured at the surface andseafloor can indicate tension build-up (wind-up) in the drill.

The systems described herein can uniquely identify acoustic signalsassociated with physical events and conclude that a particular event hasoccurred based on the detection of a unique signal. In one aspect, forexample, a method for detecting leaks in subsea equipment can includedetecting acoustic signals generated by subsea equipment using aplurality of acoustic sensor arrays that each include at least twoacoustic sensors, wherein at least a first acoustic sensor array ismounted on an outer surface of the subsea equipment and at least asecond acoustic sensor array is positioned remote from the subseaequipment. The method can further include developing a baseline ofacoustic signals produced during normal operation of the subseaequipment using a digital data processor coupled to the plurality ofacoustic sensor arrays, as well as alerting a user via a user interfacecoupled to the digital data processor if a detected acoustic signaldiffers from the baseline by at least a predetermined amount.

One of skill in the art will appreciate further variations andadvantages of the systems described herein relative to the prior art.Such variations are considered within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The aspects and embodiments of the invention described above will bemore fully understood from the following detailed description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is an illustration of one embodiment of a subsea equipmentmonitoring system;

FIG. 2 is an illustration of an alternative embodiment of a subseaequipment monitoring system;

FIG. 3 is a schematic diagram of still another embodiment of a subseaequipment monitoring system; and

FIG. 4 is a flowchart illustrating one embodiment of sensor data flowthrough a digital data processor.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the systems and methodsdisclosed herein. One or more examples of these embodiments areillustrated in the accompanying drawings. Those skilled in the art willunderstand that the systems and methods specifically described hereinand illustrated in the accompanying drawings are non-limiting exemplaryembodiments and that the scope of the present invention is definedsolely by the claims. The features illustrated or described inconnection with one exemplary embodiment may be combined with thefeatures of other embodiments. Such modifications and variations areintended to be included within the scope of the present invention.

The present invention is generally directed to systems and methods formonitoring subsea equipment that employ a plurality of non-intrusivesensors to provide a detailed view of the equipment during operation.The systems and methods described herein can be utilized to determine avariety of characteristics of the equipment being monitored, includingoperating characteristics (e.g., the speed of rotating machinery, etc.),equipment failures (e.g., internal and external leaks, cracks, etc.),and operational abnormalities (e.g., vibrations, erratic flow, pressuretransients, gas kicks, etc.). The systems and methods described hereincan also be used to identify acoustic or vibrational changes associatedwith normal wear such that preventative maintenance can be performedwhen truly necessary and before catastrophic failure of any component.

The systems and methods disclosed herein can be applied broadly to anysubsea machinery or equipment, but are described herein in connectionwith use on an oil well blowout preventer (BOP). A BOP is a piece ofsafety equipment used in subsea oil and/or gas drilling to preventuncontrolled flow from a well (i.e., a blowout). The BOP includes avertical “stack” that sits atop a wellhead on the seafloor. The stackincludes a series of hydraulically actuated shears that are meant toseal off a wellhead by force in the event of a blowout. The systemsdescribed herein can be utilized to monitor any of a number of differentspecific BOP configurations and/or architectures known in the art.

FIG. 1 illustrates a typical subsea drilling operation to extractnatural gas and/or oil from an underground reservoir 102. In particular,a drill 104 is driven through a wellhead 106 on the seafloor 108 from arig 110 floating at the sea surface 112. The drill 104 extends from therig to the wellhead 106 through a riser tube 114 that can be used tocapture the underground oil and/or gas (note that FIG. 1 is not shown toscale, as the drill 104 and riser tube 114 can extend for thousands offeet to span the depth of the ocean at the site of the well). Finally, aBOP 116 is shown in its typical location on top of the wellhead 106.

Also shown in FIG. 1 is one embodiment of a subsea equipment monitoringsystem used to monitor the BOP 116. As shown in the figure, the systemincludes a first acoustic sensor array 118 mounted on an outer surfaceof the BOP 116, a second acoustic sensor array 120 positioned remotefrom the BOP 116, and a digital data processor 122 in communication withthe plurality of acoustic sensor arrays 118, 120. Each acoustic sensorarray includes a plurality of individual acoustic sensors clusteredtogether, e.g., the arrays 118, 120 in FIG. 1 each include threeindividual acoustic sensors.

The data collected by the arrays 118, 120 can be communicated throughtethers 121, 123 to the digital data processor 122 for subsequent signalprocessing and analysis. The digital data processor 122 can provideoperators with several important monitoring capabilities, including (1)beam-forming, i.e., selective focusing on a desired portion of the BOP116 (even if no individual sensor is located at the desired portion),(2) source localization, i.e., the identification of an origin point ofa detected sound, (3) event identification, i.e., the association of aparticular acoustic signal with a physical event, and (4) trendidentification, i.e., the identification of acoustic signal changes overtime.

The ability to provide robust monitoring through signal processing andanalysis is made possible by the architecture of the acoustic sensorarrays relative to the equipment being monitored (e.g., the BOP 116). Inparticular, the system includes at least one acoustic sensor array(itself having at least two individual acoustic sensors) mounted on theequipment (either in direct contact with the equipment or immediatelyadjacent thereto) and at least one acoustic sensor array positionedremote from the equipment. This clustering of a plurality of acousticsensors both near to, and remote from, the equipment allows acousticsignals to be detected at a variety of positions and distances relativeto the equipment being monitored. In addition, the clustering andpositioning of sensors relative to the equipment being monitored canprovide better detection of certain frequencies that may not otherwisebe detected. All of the collected data can be processed in parallel bythe digital data processor 122 to, e.g., triangulate the origin of adetected sound, isolate only those sounds originating from a particularlocation, etc.

FIG. 2 illustrates an alternative embodiment of a subsea equipmentmonitoring system deployed on a BOP 202. The system includes a firstacoustic sensor array 204 mounted on an external surface of the BOP 202,as well as a second acoustic sensor array 206 positioned remote from theBOP. In this embodiment, a digital data processor 208 is positioned atthe site of the equipment being monitored, rather than on a surfacedrilling rig, as shown in FIG. 1. The digital data processor 208 can bemounted on an external surface of the BOP 202 as shown, or can bemounted to the seafloor or another piece of equipment at a locationnearby the BOP. In addition, a third acoustic sensor array 210 is showncoupled to the digital data processor 208. The third acoustic sensorarray 210, as well as any other acoustic sensor arrays that may beincluded, can add to the data collected by the first and second acousticsensor arrays 204, 206.

Each of the sensor arrays 204, 206, 210, can include at least twoindividual acoustic sensors. For example, in the embodiment shown inFIG. 1, the acoustic sensor arrays 118, 120 each include threeindividual acoustic sensors, while the arrays 204, 206, 210 each includefive individual sensors. The particular number of sensors used in anarray can be determined based on available space, as well asrequirements for power, communication bandwidth, etc. Further, any of avariety of known acoustic sensors (e.g., hydrophones, etc.) can beutilized in the arrays 204, 206, 210. For example, in some embodiments,piezoelectric ultrasonic acoustic sensors can be employed in theacoustic sensors arrays.

The individual sensors in an array can be arranged in a variety ofconfigurations relative to one another. For example, the individualsensors in an array can be rigidly fixed to one another in a number ofshapes (e.g., disposed in a straight line as shown in FIG. 2), or theycan be coupled to one another in a manner that permits relative motion(e.g., by connecting them with a flexible wire or tether). In addition,a distance between the individual sensors in an array can be uniform orvaried, and can vary among different arrays in certain embodiments.

Moreover, each of the individual sensors in an array can be housedtogether or individually. In some embodiments, housing sensorsindividually can provide an additional advantage in that water ingressinto one housing will not cause a failure of all sensors in the array.Separate sensor housings can therefore provide redundancy for the arrayand can allow the monitoring system to continue operating even ifseveral individual sensors fail over time.

Acoustic sensor arrays, such as the array 204, can be mounted on the BOP202 in a variety of manners known in the art. For example, in someembodiments the array 204 can be mounted to the BOP 202 using bolts ormagnets. In such an embodiment, the array 204 can act as a vibrationsensor as well, given its rigid attachment to the BOP 202. In otherembodiments, however, the array 204 can be mounted on the BOP 202 with asmall amount of clearance between the individual sensors of the arrayand the BOP. Positioning the array 204 immediately adjacent to the BOP202 in this manner will have little effect on its ability to detectsounds, given the transmission properties of water. Finally, in stillother embodiments, a subset of the individual sensors of a sensor arraycan be rigidly mounted on the BOP, and a subset of the individualsensors can be mounted on the BOP at a position immediately adjacentthereto. All of these configurations can be varied across a number ofarrays (or individual sensors within an array) to provide enhancedacoustic detection capability.

Other acoustic sensor arrays, such as the array 206, can be positionedremote from the BOP 202. In the illustrated embodiment, the acousticsensor array 206 is freely suspended a distance from the BOP 202, but iscoupled to the digital data processor 208 by a tether 212. As notedabove, the acoustic sensor array 206 can have a variety ofconfigurations, including any number of individual acoustic sensorsarranged in a variety of geometries (e.g., straight line, circle,sphere, etc.). In addition, the array 206 can be suspended in anydesired orientation (e.g., vertical, horizontal, diagonal, etc.)relative to the BOP 202 of the seafloor. For example, in addition to thetether 212 that couples the array 206 to the digital data processor 208,additional ropes, cables, or other tethers can be used to anchor thearray 206 to the seafloor, the BOP 202, or other equipment in a desiredlocation and orientation.

Any acoustic sensor array deployed to monitor subsea equipment can be incommunications coupling with the digital data processor performingsignal processing and analysis. As noted above, the digital dataprocessor (or processors) can be positioned on the seafloor near theequipment being monitored (e.g., as shown in FIG. 2), or at the surfaceon a drilling rig or other above-water machinery (e.g., as shown in FIG.1). Coupling between the acoustic sensor arrays and the digital dataprocessor can be accomplished in a variety of manners, including the useof cable tethers (e.g., tether 212) that house power delivery andcommunication wires. Exemplary wires can include traditional copper (orother conductive metal) wiring, or fiber-optic cabling. In someembodiments, an oil-filled tether hose can be used to provide a barrieragainst water intrusion and to equalize pressure on the wires, therebypreventing uneven compression of copper and/or fiber-optic wires withinthe tether.

In other embodiments, however, wireless communications can be utilizedto reduce the number of wires extending around the BOP 202 or otherequipment being monitored. Wireless communication methods suitable foruse in a subsea environment can include acoustical or short-range radiocommunications. In embodiments where wireless communications areemployed, each acoustic sensor array can also include a battery coupledthereto to provide power for the individual acoustic sensors and anyrequired wireless transmitters.

In some embodiments, the particular form of communications couplingemployed can influence the position of the digital data processor. Forexample, if copper wiring or short-range wireless communications areemployed, bandwidth and/or transmission distance limitations can requirethe digital data processor to be located on the seafloor, as shown inFIG. 2. If fiber-optic cabling is employed, however, large amounts ofraw data can be transmitted rapidly to a digital data processorpositioned at the ocean's surface, as shown in FIG. 1. In still otherembodiments, a repeater positioned on the seafloor can be utilized,e.g., to collect short-range wireless signals and communicate data tothe surface via a single fiber-optic connection (similar to the singleconnection 213 that couples the digital data processor 208 to a surfacedrilling rig).

In certain embodiments, a subsea equipment monitoring system can alsoinclude one or more individual acoustic sensors mounted on the equipmentbeing monitored. For example, FIG. 2 shows several individual acousticsensors 214 mounted on the BOP 202 at various locations. Theseindividual acoustic sensors can be identical to the individual acousticsensors used in each of the acoustic sensor arrays 204, 206, 210, andcan be mounted on the BOP 202 in the same manner as the first acousticsensor array 204. The individual sensors 214 can be positioned nearindividual components of the BOP 202, such as a valve, bearing, seal,etc., and can provide localized detection of sound and/or vibrationoriginating from the component. This data can be combined with datacaptured from the acoustic sensor arrays to provide better localizationof sound origination (e.g., by allowing for discrimination between twoseals located close to one another, etc.). Moreover, it is also possiblethat one or more individual acoustic sensors can be positioned remotefrom the equipment being monitored to provide additional input to thedigital data processor.

In still other embodiments, other types of sensors can be integratedinto a subsea equipment monitoring system along with the plurality ofacoustic sensor arrays and any additional individual acoustic sensors.FIG. 3 illustrates one embodiment of a subsea equipment monitoringsystem 300 that includes a digital data processor 302 as well as a firstacoustic sensor array 304, a second acoustic sensor array 306, and anindividual acoustic sensor 308. The system further includes a camera310. The camera 310 can be mounted on the seafloor near the BOP 202, forexample, or can be disposed on a remotely operated vehicle (ROV)positioned near the BOP 202. In addition, any other type of sensor canbe used in combination with the system 300, e.g., pressure andtemperature sensors, sensors positioned on a surface drilling rig, etc.

Regardless of their particular type or position, data captured byadditional sensors can be incorporated into the signal processing andanalysis conducted by the digital data processor 302. For example, inone embodiment data gathered by the acoustic sensors of the subseaequipment monitoring system can be used to confirm or quality-check datagathered by an additional sensor, such as the camera 310. The camera 310may indicate, for example, that the BOP 202 or other equipment isvibrating, when in fact it may be a faulty camera mount that is creatingvibration. Data gathered from the acoustic sensor arrays mounted on, andpositioned remote from, the BOP can be utilized to confirm or refute thecamera's indication of vibration at the equipment.

The digital data processor 302 can have a number of differentconfigurations. For example, the digital data processor 302 can be ahardened computing device configured for placement on the seafloor near(or on) the BOP, or it can be a more traditional computing devicedisposed on a surface drilling rig or a ship. The digital data processor302 can be a single computing device, or it can include a number ofdifferent digital data processors networked together. Furthermore, thedigital data processor 302 can be coupled to a digital data store 314 sothat analysis, historical trends, and other data can be accessed andupdated as necessary. Exemplary digital data stores include individualsolid state or other types of digital storage media, networked digitalstorage repositories, etc. The digital data processor 302 can also becoupled to a user interface device 316 to allow interaction with one ormore operators. For example, in some embodiments a digital dataprocessor 302 can be coupled to a display screen, status board,keyboard, mouse, etc. to allow user interaction with the digital dataprocessor 302. Other exemplary user interface devices can includewarning lights, audio speakers, etc.

The digital data processor 302 utilizes multivariate signal processingto analyze data collected by all the acoustic sensor arrays, individualacoustic sensors, and other sensor types to isolate signals of interest.With respect to the acoustic sensor data, the digital data processor 302can create multi-resolutional sensor clusters by combining acoustic datafrom subsets of the plurality of sensors in various ways. For example,in one embodiment a generic set of N acoustic sensors spread across aplurality of acoustic sensor arrays and distributed in three-dimensionalspace, the set can be divided into K subsets of minimum four sensors,where K is defined by the binomial coefficient (N, 4). Furthermore, eachsubset can be selected such that it spans three-dimensional space, andall sensors can be time-synchronized.

The resulting subsets can be processed in parallel to achieve a systemwith multi-resolutional properties. That is, a small sensor array (i.e.,a short distance between individual sensors) can suffer from poorresolution on low frequencies and instability in distance estimation.Conversely, small sensor arrays can be better suited for high frequencydetection because of spatial aliasing. Large sensor arrays (i.e., a longdistance between individual sensors) can behave in an inverse fashion,exhibiting enhanced spatial resolution on low frequencies and improvedperformance in distance estimation. Importantly, the overall performanceof the system will overcome difficulties of individual sensor arrays bycombining them in various fashions, resulting in a multi-resolutionalsystem.

As mentioned above, two primary capabilities provided by the signalprocessing of the digital data processor 302 are beam-forming andsource-localization. In beam-forming, the system selectively focuses ona portion of the equipment being monitored to isolate sounds originatingfrom that portion. This is accomplished in the digital data processor302 by introducing appropriate phase delays to digitized raw sensorsignals before summation in order to focus on a point inthree-dimensional space, while at the same time ignoring contributionsfrom other interfering sources at other locations in three-dimensionalspace. However, beam-forming theory in general reaches far beyond thisbasic concept and more optimum methods such as adaptive beam-forming canalso be introduced. An adaptive beam-former is a dynamic system thatautomatically adapts to the incoming signals in order to maximize orminimize a desired parameter. Source-localization is essentially theinverse of beam-forming, wherein the origin point of a detected sound isdetermined. This is accomplished in the digital data processor 302 byestimating the phase delays of incoming acoustic sensor signals andmapping them onto geographical coordinates.

The digital data processor can also determine operating characteristicsof the equipment being monitored, and compare those operatingcharacteristics with one or more operating characteristics measured at adifferent location, e.g., above the surface of the water. Referring toFIG. 1, for example, the digital data processor 122 can be configured todetermine the rotating speed of the drill 104 disposed within the BOP116 using detected acoustic signals from the plurality of acousticsensor arrays 118, 120. The digital data processor 122 can also beconfigured to determine the rotating speed of the drill 104 at alocation above a surface of the sea, e.g., using rotation sensor 124mounted on the drilling rig 110. The rotating speed above the surface ofthe water can then be compared to the rotating speed at the BOP. Asignificant difference in these values can indicate that tension isbuilding in the drill shaft. If the difference between the sub-surfaceand top-side measurements is significantly large (e.g., exceeds apredetermined value), an operator can be alerted or other action can betaken (e.g., drill shut down, throttle adjustment, etc.). Of course,rotating speed of a drill passing through a BOP is just one example ofan operating characteristic that can be determined by the subseaequipment monitoring system, and any of a variety of othercharacteristics can also be determined and compared to measurementstaken at different locations in the drilling operation.

As noted above, in addition to selectively focusing on portions ofequipment being monitored or determining operating characteristics ofsubsea equipment, the digital data processor can also identify physicalevents based on their unique acoustic signals and track acoustic trendsover time to note departures from a baseline profile. For example, andas shown in FIG. 4, data 402 from all of the acoustic sensors of theplurality of sensor arrays, individual sensors, and any other sensorscoupled to the system, can be routed in parallel to an event processingsystem 401 and a trend processing system 403.

The event system 401 can be configured to analyze sudden events oflimited duration, e.g., closing and opening of BOP shear rams. An eventvalidator 404 can process the data to rule out or confirm the presenceof an event based on a predetermined set of rules. For example, atypical rule might require spatial stationarity, i.e., that originationsounds come from a stationary location, in order to qualify as an event(e.g., if acoustic signals are indicating that a particular seal hasfailed, the signals should continue to originate from the location ofthe failed seal). To determine spatial stationarity, the digital dataprocessor can utilize its selective focusing and source-originationcapabilities. For example, spatial stationarity can be measured bycalculating the source of the event multiple times over a period oftime. The standard deviation of these measurements can indicate if thesource of the event is moving or not.

After determining that an event has occurred (or is occurring), an eventpreprocessor 406 can process and format the acoustic signals of theevent. In some embodiments, the acoustic signals of the event can beprocessed into a signature of the event that includes a temporaldistribution and a spatial distribution of the acoustic signals of theevent. The temporal distribution can be, for example, a sparserepresentation such as a time-scale/time-frequency/time-Melrepresentation (e.g., using the Wavelet and/or Short-Time FourierTransform) that describes the features of the event in an acousticalsense. The spatial distribution can be, for example, estimated usingarray processing including the cross-spectral matrix, complex analyticcross-correlations, phase transform, and a lag-to-angle andlag-to-distance mapping. In some embodiments, the Karhunen-LoèveTransform can be applied to both distributions to reduce dimensionalityand provide for easier classification and/or clustering of similarevents.

An event comparator 408 can identify or classify the acoustic signalsdetected, or their computed signatures, using an event library 410 thatincludes a listing of physical events and their known associatedacoustic signals or signatures. If the detected event matches one ofthose already stored in the event library 410, the event comparator 408can update the system status 412 by reporting the occurrence of theevent and recommending or initiating a response action. This can bedone, for example, using the user interface device 316 shown in FIG. 3.If, on the other hand, the detected acoustic signals or computedsignature do not match any of the events stored in the event library410, the detected acoustic signals and/or their computed signature canbe stored in the event library 410 for later classification andassociation with a physical event. The event comparator 408 can beimplemented using classification and machine learning theory, includingdiscriminant analysis (DA) techniques or pattern matching algorithms,such as the dynamic programming (DP) algorithm, or, e.g., using aK-nearest-neighbors approach.

In parallel with the event detection and classification system 401, thedigital data processor can also execute a trend system 403 based on thedata collected by the acoustic sensor arrays. The trend system 403 canexecute continuously independent of any special events found in thecollected data. The trend system can include a trend preprocessor 414that forms a baseline of acoustic signals—or data calculatedtherefrom—produced during normal operation of the subsea equipment. Thetrend preprocessor can calculate a number of trends from the input datagiven a prescribed configuration. For example, computed trends caninclude complete frequency spectra, energy in certain frequency bands,positions of signal sources, level of spatial stationarity, etc. Thebaseline of acoustic signals, as well as any other computed data ortrends, can be stored in a historical trend library 416. A trendcomparator 418 can compare the detected acoustic signals (or trend datacomputed therefrom) to baseline acoustic signals (or trend data computedtherefrom) to determine if the monitored equipment is operating in anormal state or not. If a difference between the detected values and thebaseline values exceeds a predetermined amount, the system status 412can be updated to alert an operator.

The combination of event detection and trend monitoring can allow thesubsea equipment monitoring systems described herein to detect a numberof operating abnormalities of subsea equipment. Examples include thedetection of internal and external leaks, erratic flow, gas kicks(flow-induced vibrations from the annulus or drilling string), anderratic pressure transients, among others. Of particular note is thatthe systems described herein can detect the presence of worn seals orbearings prior to catastrophic failure of these components. That is, theacoustic signals emitted by a seal can change over time (e.g., deviatefrom a baseline acoustic signal) as the seal wears and the subseaequipment monitoring systems described herein can detect this change.Prior art acoustic monitoring systems are not able to provide the levelof detail necessary to detect this change. The ability to detectindividual seal wear can allow operators to plan preventativemaintenance in a more intelligent manner based on actual wear and tearof the subsea equipment rather than a set maintenance schedule. Such amodification has the potential to increase both the safety andefficiency of subsea drilling operations or other activities.

The subsea equipment monitoring systems described herein also provide anability to detect cracks forming in the subsea equipment at a very earlystage. In particular, developing cracks, e.g., in the housing of a pieceof equipment, can create sudden transient acoustic signals. Prior artacoustic monitoring systems are not able to detect these transientsignals that indicate the early stages of crack formation. Note that theinability of prior art systems to detect these transient signals canstem from either an inability to detect the signal at all (i.e.,imprecise acoustic detection), or an inability to determine that thetransient represents a departure from the normal operation of theequipment (i.e., no trend monitoring).

Seal wear and crack formation detection are just two examples ofimprovements over prior art subsea monitoring systems. Other advantagesof the systems and methods described herein include the use ofexternally-mounted, non-intrusive arrays of acoustic sensors. Usingnon-intrusive arrays allows the monitoring system to be servicedseparately from the subsea equipment, which avoids the need to shut downa drilling operation or raise the subsea equipment to repair themonitoring system. In addition, the use of arrays having two or moreindividual acoustic sensors can provide redundancy to the system in theevent that one or more sensors fails, again allowing service of amonitoring system to be performed at the most convenient and efficienttime for the operator. Still further, the use of non-intrusive acousticsensor arrays allows for easy retro-fitting of subsea equipment suchthat the monitoring system does not require the purchase andinstallation of new subsea equipment.

The increased visibility of the subsea equipment during operation allowsoperators to increase the safety, better address failures, and increaseefficiency by optimizing equipment down-time for preventativemaintenance. As noted above, the embodiments disclosed herein havefocused on monitoring of a BOP, but the subsea equipment monitoringsystems described herein can be used with almost any subsea operationthat produces unique acoustic signals. BOP-specific examples includemonitoring the landing of a BOP on a wellhead during initialconstruction of the well, operation of shearing rams to seal the well,confirmation that well flow has been stopped after activation ofshearing rams, characterization of flow within the BOP, etc. Inaddition, the systems described herein can be employed on any of avariety of other subsea equipment, including solenoid valves, pumps,compressors, etc.

The advantages of the systems described herein derive from the use of aplurality of acoustic sensor arrays, where at least a first array ismounted on equipment being monitored and at least a second array ispositioned remote from the equipment being monitored. A digital dataprocessor, when coupled with this arrangement of acoustic sensor arrays,can selectively analyze signals from the set of acoustic sensor arraysto provide the powerful monitoring capabilities described above.

All papers and publications cited herein are hereby incorporated byreference in their entirety. One skilled in the art will appreciatefurther features and advantages of the invention based on theabove-described embodiments. Accordingly, the invention is not to belimited by what has been particularly shown and described, except asindicated by the appended claims.

What is claimed is:
 1. A system for monitoring subsea equipment,comprising: a plurality of acoustic sensor arrays that each include atleast two individually housed acoustic sensors configured to receive anacoustic signal generated by subsea equipment being monitored, whereinat least a first acoustic sensor array is mounted on an outer surface ofthe subsea equipment and at least a second acoustic sensor array ispositioned remote from the subsea equipment; a digital data processor incommunication with the plurality of acoustic sensor arrays, the digitaldata processor being configured to process data from selected sensors ofthe plurality of acoustic sensor arrays, the data representing theacoustic signal, the digital data processor further configured to:monitor, using beam forming, a portion of the subsea equipment fromwhich the acoustic signal originates and ignore interfering acousticsignals originating from other portions of the subsea equipment, anddetermine, based on the acoustic signal, a point of origin of theacoustic signal within the portion of the subsea equipment, wherein thedigital data processor is coupled to the first acoustic sensor array bya first tether, wherein the digital data processor is coupled to thesecond acoustic sensor array by a second tether, wherein the firstacoustic sensor array is coupled to a free end of the first tether andis in direct contact with the subsea equipment being monitored, andwherein the second acoustic sensor array is coupled to a free end of thesecond tether and freely suspended from the second tether; and a userinterface coupled to the digital data processor, the user interfaceconfigured to alert a user to the acoustic signal received by theacoustic sensor arrays and to the point of origin within the portion ofthe subsea equipment.
 2. The system of claim 1, wherein the digital dataprocessor is located below a surface of the sea, and the plurality ofacoustic sensor arrays includes at least a third acoustic sensor arrayattached to the digital data processor.
 3. The system of claim 1,further comprising at least one individual acoustic sensor mounted onthe outer surface of the subsea equipment.
 4. The system of claim 1,wherein the first acoustic sensor array mounted on the subsea equipmentis any of bolted and magnetically coupled to the subsea equipment. 5.The system of claim 1, wherein the first acoustic sensor array is fixedrelative to the subsea equipment, and wherein the second acoustic sensorarray is moveable relative to the subsea equipment.
 6. The system ofclaim 1, wherein the second tether provides power to the second acousticsensor array and provides communication between the second acousticsensor array and the digital data processor.
 7. The system of claim 1,further comprising an image capture device.
 8. The system of claim 1,wherein the subsea equipment is an oil well blow out preventer.
 9. Thesystem of claim 1, wherein each of the plurality of acoustic sensorarrays are configured to communicate with the digital data processorwirelessly.
 10. The system of claim 1, wherein the digital dataprocessor is further configured to identify an event based on acomparison of a detected acoustic signal to a library of acousticsignals associated with one or more known events.
 11. A method fordetecting leaks in subsea equipment, comprising: monitoring, using beamforming, a portion of the subsea equipment to isolate acoustic signalsoriginating from the portion of the subsea equipment from interferingacoustic signals from other portions of the subsea equipment; detectingacoustic signals generated by subsea equipment and originating from theportion of the subsea equipment using a plurality of acoustic sensorarrays that each include at least two individually housed acousticsensors configured to receive the acoustic signals, wherein at least afirst acoustic sensor array is mounted on an outer surface of the subseaequipment and at least a second acoustic sensor array is positionedremote from the subsea equipment; developing a baseline of acousticsignals produced during normal operation of the subsea equipment using adigital data processor coupled to the plurality of acoustic sensorarrays, the digital data processor coupled to the first acoustic sensorarray using a first tether and coupled to the second acoustic sensorarray using a second tether, the first acoustic sensor array coupled toa free end of the first tether and in direct contact with the subseaequipment, and the second acoustic sensor array coupled to a free end ofthe second tether and freely suspended from the second tether; andalerting a user via a user interface coupled to the digital dataprocessor if a detected acoustic signal originating from the portion ofthe subsea equipment differs from the baseline by at least apredetermined amount.
 12. The method of claim 11, further comprisingdetermining a point of origin of the detected acoustic signal thatdiffers from the baseline signature by at least the predeterminedamount.
 13. The method of claim 11, wherein the subsea equipment is anoil well blow out preventer.
 14. The method of claim 11, furthercomprising: searching a digital data store containing a library ofevents and associated acoustic signals for an acoustic signal thatmatches the detected acoustic signal; if a match is found, alerting auser of the event associated with the detected acoustic signal; and if amatch is not found, storing the detected acoustic signal in the digitaldata store for future association with an event.